Television tube



Feb. 20, 194%. SCHLEslNGER, 2,191,415

TELEVISION TUBE A Filed June 22, 1956 30 V 3 200? m 7500 V jean V F/y. m

Patented Feb. 20, 1940 TELEVISION E Application June 22, 1936, Serial No. 86,607 In Germany July 6, 1935 3 Claims.

It is known that upon the deflection of bundles of cathode rays of large cross-section, such as occur in certain cases in high-vacuum tubes, there may be a considerable lack of sharpness at the edges of the area swept over on the image screen by the beam. It is known that this lack of sharpness at the edges which is caused by different degrees of deflection of the individual part-rays of the bundle, is in general greater in the case of electrostatic deflection than in the case of magnetic deflection. Further, it has been set forth in earlier applications of the applicants that these faults in the sharpness of the edges may be considerably reduced by applying the deflecting potentials to the two deflecting plates in reverse phase. The extent of the marginal sharpness fault still remaining depends primarily on the ratio between the diameter of the ray and the minimum spacing of the plates. On the other hand, the sensitivity of a deflecting condenser is also limited by the thickness of the bundle of rays. It would accordingly represent an improvement if electron-optical systems could be so produced that the bundle of rays possesses a cross-section as small as possible in the region of the deflecting plates. With a given spacing of the plates it would then be possible greatly to reduce the lack of sharpness at the edges, or it would be possible to increase the sensitivity by decreasing the spacing of the plates. The subject matter of the invention is an electron-optical arrangement, which enables these advantages to be obtained. In its external form this arrangement is identical with the television tube relating to which a patent application has already been filed under Serial Number 49,953, filed November 15, 1935, Pater. No. 2,126,287, dated August 9, 1938 (see Fig. 2 of that prior application). An essential feature in the pi esent case is the adjustment of the passage of the rays such that the narrowest point of the bundle of rays is disposed at the point of deflection, in the manner which will be described.

The tube comprises two concentration lenses, of which the rear one situated at the cathode acts as a condenser lens (illuminating lens) whilst the front one causes the reproduction of a diaphragm (reproducing lens).

In the drawing Fig. 1a shows with the symbols usual in the optical art the optical arrangement corresponding to the electronic tube shown in Fig. 1b.

In Fig. lb, l is a glow-head, which is heated by the spiral 2 and carries the oxide surface 3 in a boring. If the bias of the cylinder 6 is varied and is made more negative, the refractive powers of this lens are increased. There may then be observed a point of constriction in the passage of the rays. moving more and more away from the screen towards the cathode. In this experiment the anode is directly connected wtih the tubular member, so that a second refractive force does not exist. In accordance now with the invention the bias of (5 is so adjusted that this point of maximum constriction is situated in the vicinity of the anode or between the deflecting plates. There is then in the first plate obtained the advantage that the deflection remains sharp without loss of sharpness up to the edges. If now the second lens is introduced by imparting to the tubular member 8 a bias which is negative in relation to the anode 9, there can no longer be obtained a sharp image of the cathode on the luminous screen i l, but blurred patches are formed on the screen. A sharp image point is not obta ned until a diaphragm 7 having a small aperture is provided at the rear end of the tubular member 3. It has been found that the reproduction of this diaphragm aperture on the screen is also improved by adjusting the lens 6 as taught by this invention, as it is much more simple to 5 reproduce sharply a narrow bundle of rays than a wide one, and with the adjustment of the illuminating lens 6 in accordance with the invention the point of smallest cross-section of the ray is situated right in the region of the main lens 8/9.

A third advantage resides in the fact that losses in the intensity of the ray current by reason of electrons striking the metallic portions of the optical system are completely avoided, the ray being thin.

The boring for the oxide surface is of approximately the same size as the boring in the diaphragm l. ..t would be useless to select a large oxide surface 3 insofar as with a given adjustment of the focus of the condensing system 5, B, I there is situated over the diaphragm I a given cross-section of the ray dependent on the size of the spot of oxide 3, and with an increase in the size of the spot of oxide 3, and with an increase in the size of this oxide surface there would 00- 45 our merely unnecessary losses at the diaphragm l and not an increase in the light intensity on the screen Hi.

The emission of the cathode spot 3 is controlled by means of a control element 4. The suction 0 field is produced by a protective anode 5. By virtue of this electrode the ray current entering the optical path is made independent of all adjustments of the optical system, so that reactions from the optical adjustments on the energy of radiation are avoided. In accordance with the invention, a small advance 4 beyond 4 is provided at the guide cylinder surrounding the cathode, in which manner there may be obtained a weak preliminary concentration of the ray, and there is ensured a practically parallel entry of the ray into the actual optical system. However, the advance 4 may also be dispensed with, as in the case of the earlier application, without the advantages of the optical system following thereon as obtained according to the invention being appreciably reduced.

The suctional anode 5, the diaphragm I having the aperture to be electron-optically reproduced and the main anode 9 having fixed positive biases applied thereto. The suctional anode determines the working point (bias) of the control grid 4'. Said suctional anode requires to be positive only to such extent that the maximum ray current with which the same operates obtains with a still negative bias of the grid (control electrode) 4. The advantage then results that the grid remains currentless and there is no loss of ray current. With spacings of approximately 3 mm. between grid 4' and suctional an ode 5 and grid apertures of approximately 1 mm.

diameter biases of approximately 200 to 300 volts are sufiicient for controlling the complete emission without grid current up to approximately 1 mA. The anode 9 in the same manner as the biases for the plates and the bulb space or the coating [5 on the wall is raised to the highest potential available, for example 4,000 volts. The diaphragm 1 may be provided with a potential 1 which is between the two stated ones, in which manner, from the electron-optical point of View, there is obtained the advantage that the size of the image point is reduced. It has been found in practice, however, that more particularly when employing very powerful ray currents the ray space charge is more readily overcome when the diaphragm I is connected with a comparatively high positive bias, and preferably even with the highest potential, viz., directly with the anode 9. With the insulation according to the invention between the diaphragm cover '3 and the tubular member 8 the bias of the diaphragm may be freely selected between the stated limits.

The which call for adjustment are the biases of the two cylinder electrodes 6 and 8. The bias of 8 determines the point at which there appears the reproduction of the cathode surroundings. In Fig. 1a, the optical analogy of this tube, there is shown the manner in which the passage of the rays should be disposed in accordance with the invention. The cathode 3 is replaced by a light source 3a of finite expanse. At the place of the first cylinder 6 there is located an equivalent collecting lens 5a. At the place of the hood of the tubular member it there is located the re producing lens 8a, and the narrowest point of the bundle of rays should be situated in the anode space or at the point where the deflecting plates have their smallest spacing, i. e., at 9a. According to the invention, the focal distance of the condensing lens Ba is so adjusted that the image of the hot cathode 3a substantially coincides as regards its location with the main lens 8a or with a region in the vicinity thereof. This is because the image of the cathode surroundings is identical with the narrowest part of the bundle of ray as formed by 6a alone. The size of this image depends on the potentials of the electrons in the space between 3 and 6 on the one essential biases of the optical system r hand and in the space between 6 and 8 on the other hand and also on the corresponding geometric spacings. The speed in the preliminary space 3, B should be as small as possible, that in the tube space 6, 8 as high as possible. With a cathode spot of approximately mm. diameter there is obtained under the stated potential conditions at a distance of 100 mm. (length of 8) and with a spacing (3, 6) of merely 20 mm. an image approximately 2 mm. in diameter. A still smaller image is obtained if the bias of the diaphragm 7 is increased, or if the bias of the screening grid 5 is reduced. According to the invention, 5 and s may also be connected together and their biases regulated in common.

In Fig. 1a the image of the cathode is found at the place of the lens 8a, according to the simple law of spacing of the optical system, withasize I6. This size is to be reduced by the potential factor i. e., the quotient of the stated speeds. There thus results the image ll. If a lens produces an image of an object located at the same place as the lens itself, the object and the image remain at the same point. The object here in question is the image of the cathode produced by the first lens. The second lens accordingly produces an image of said image and consequently of the cathode itself at its own place. At another point, for example on the luminous screen, a sharp image of the cathode is accordingly no longer obtainable. The tubes according to the invention, which project the reproduction of the cathode by means of a first lens into the main] lens, accordingly require to derive the image point on the screen from another object, via, from the diaphragm la. The diaphragm la, in the manner know per se, is reproduced by the main lens Ed on the luminous screen in the form of an image point of the size 18. The size I3 found in accordance with the well known law of common glass optics from the different distance requires in turn to be multiplied by the potential factor of the electron speeds at the diaphragm la and at the luminous screen in. This factor, however, in the case of a high positive bias of the diaphragm l is not very much smaller than 1. In practice, with a distance ratio of 1:3 and a bias of the diaphragm 1 equal to that of the anode 9, there is obtained with a diaphragm of .4 mm. diameter an image point approximately 1 mm. in diameter.

Since the ray in the region 9a of the plates has merely a cross-section of 2 mm., there may be employed very sensitive plates with a relative spacing of .3-4 mm. It has been found that with a push-pull deflection and a ratio of 2:1 between plate spacing and the thickness of the ray a lack of sharpness at the edge no longer occurs in practice. The optical system shown exhibits ray current losses only at the diaphragm 1. All later diaphragm apertures are traversed by the ray without loss, as the cross-section of the ray is reduced in size towards the screen. The guiding of the ray in accordance with the invention accordingly represents the opposite to a two-lens optical system without an intermediate diaphragm with reproduction of the cathode on the luminous screen. An optical system of this kind, such as describedand claimed by the applicant in the application numbered S. N. 86,608, filed June 22, 1936, Patent No. 2,123,161,

dated July 5, 1938, exhibits at the point of the last anode not the smallest but the largest crosssection of the ray. In this case, in accordance with the law laid down by the present invention that the spacing of the plates should amount to twice the cross-section of the ray, it is impossible to obtain with given sharpness of the edges a sensitivity equal to that in the present tube.

I claim:

1. Electric apparatus more particularly for television purposes comprising a cathode ray tube including a diaphragm having an aperture, means including a hot cathode for producing and controlling a bundle of electrons and guiding said bundle through said aperture, an image screen, an electron lens for producing on said image screen a sharp electron image of said aperture, a further electron lens disposed between said cathode and said diaphragm to contract said bundle to a maximum degree in the region of the first said electron lens, means for providing the aforementioned means, said diaphragm and said lenses with operating potentials and means for adjusting at least one of said potentials to control the focus of said further electron lens.

2. In an arrangement comprising a cathode ray tube including a hot cathode having an emitting spot, an electron-optical system comprising a first lens and a second lens, a diaphragm having a fine aperture situated between said lenses, deflecting elements mounted in the neighborhood of said second lens, and an image screen: adjustable means for so energizing said first lens as to produce in the region of said second lens, in the absence of the same, a maximum constriction of the cathode ray, and means for s0 energizing said second lens as to focus said aperture upon said screen.

3. In an arrangement comprising a cathode ray tube including a hot cathode having an emitting spot, an electron-optical system comprising a first lens and a second lens, a diaphragm having a fine aperture situated between said lenses, deflecting elements mounted in the neighbourhood of said second lens, and an image screen; adjustable means for so energizing said first lens as to produce in the region of said second lens, in the absence of the same, a maximum constriction of the cathode ray, and means for so energizing said second lens as to focus said aperture upon said screen, each of said lenses being provided, at its side facing said cathode, with a diaphragm connected to a fixed potential.

KURT SCI-ILESINGER. 

